1. Field of the Invention
This invention relates to a method for fabricating a color solid-state image sensor of the type having an overlying passivation layer onto which color filters are fabricated.
2. Description of the Prior Art
FIG. 1 shows a schematic representation of a cross-section of a support on and in which color solid-state imaging devices have been fabricated. The support is comprised of photosensing elements 1 and bonding pad areas 2. A passivation layer 3 covers the radiation-sensitive area but is removed from the bonding pad areas. Color filters 4, each of which is composed of one or more layers of a dyed coating, are fabricated over the passivation layer in registration with the photosensing elements.
FIGS. 2a-2d illustrate the different steps of one method for making such a color solid-state image sensor. According to this method, the portion of the passivation film that covers the bonding pad areas is removed prior to the coating of the color filter layers. A major disadvantage to this approach is that the bonding pad metallization is exposed to all of the color filter processing including the cleaning process, coating solutions, dye baths, etc. As a result, the chemicals that are used in these process steps may either attack and corrode the bonding pad metal during color filter fabrication, or they may become trapped in the bonding pad area and cause reliability problems as they interact with the metal over time. Also, the additional topography generated as a result of the passivation layer being removed over the bonding pads may contribute to coating non-uniformities in the subsequent color filter layers.
The following two patents describe the patterning of a layer beneath color filters:
U.S. Pat. No. 4,786,819 granted to Tei et al describes a method for fabricating a contact type color image sensor comprising the steps of forming a plurality of photoelectric converting elements having light receiving areas on a substrate; forming a passivation layer on selected light receiving areas, forming a light shielding film on said passivation film by depositing a thin film of metal and forming a color filter on other selected light receiving areas of each photoelectric converting element by forming a dyeable polymer layer and dyeing said dyeable polymer layer. The main drawback of such a method lies in its complexity. Furthermore, nothing is clearly described in this patent as regards to the patterning step used to make contact openings in the passivation layer that is under the color filters.
U.S. Pat. No. 4,783,691 issued to Harada suggests cutting through a color filter protection layer, a silicon carbide layer and an amorphous silicon photoconductor using an "ordinary etching technique". The method used for forming the pattern or performing the etch is not presented. Given the chemical diversity of the materials which have to be removed, such a process would be rather complex.